It is noted that growth hormone deficiency (GHD) in adults show a reduced sense of psychological well-being and are frequently found to have impaired cognitive functioning. It is also known that mood and cognitive functioning are positively related to the level of insulin-like growth factor-I (IGF-I), a serum marker for growth hormone (GH) status. More specifically, IGF-I levels appear to be related to cognitive status, short-term memory performance, and cognitive flexibility. GH substitution in GH-deficient patients improves cognitive functioning, as assessed by tasks measuring attention, memory, and perceptual motor skill. Moreover, GH treatment has been found to reduce the concentration of homovanillic acid, a dopamine metabolite, in cerebrospinal fluid. As the hippocampus is known to contain high levels of dopamine, this structure may be particularly affected by GH treatment. Involvement of the aforementioned brain areas in cognitive functions might explain the connection between GH treatment and neuropsychological functions.